1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Detect Hung Task 4 * 5 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state 6 * 7 */ 8 9 #include <linux/mm.h> 10 #include <linux/cpu.h> 11 #include <linux/nmi.h> 12 #include <linux/init.h> 13 #include <linux/delay.h> 14 #include <linux/freezer.h> 15 #include <linux/kthread.h> 16 #include <linux/lockdep.h> 17 #include <linux/export.h> 18 #include <linux/panic_notifier.h> 19 #include <linux/sysctl.h> 20 #include <linux/suspend.h> 21 #include <linux/utsname.h> 22 #include <linux/sched/signal.h> 23 #include <linux/sched/debug.h> 24 #include <linux/sched/sysctl.h> 25 26 #include <trace/events/sched.h> 27 28 /* 29 * The number of tasks checked: 30 */ 31 int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; 32 33 /* 34 * Limit number of tasks checked in a batch. 35 * 36 * This value controls the preemptibility of khungtaskd since preemption 37 * is disabled during the critical section. It also controls the size of 38 * the RCU grace period. So it needs to be upper-bound. 39 */ 40 #define HUNG_TASK_LOCK_BREAK (HZ / 10) 41 42 /* 43 * Zero means infinite timeout - no checking done: 44 */ 45 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT; 46 47 /* 48 * Zero (default value) means use sysctl_hung_task_timeout_secs: 49 */ 50 unsigned long __read_mostly sysctl_hung_task_check_interval_secs; 51 52 int __read_mostly sysctl_hung_task_warnings = 10; 53 54 static int __read_mostly did_panic; 55 static bool hung_task_show_lock; 56 static bool hung_task_call_panic; 57 static bool hung_task_show_all_bt; 58 59 static struct task_struct *watchdog_task; 60 61 #ifdef CONFIG_SMP 62 /* 63 * Should we dump all CPUs backtraces in a hung task event? 64 * Defaults to 0, can be changed via sysctl. 65 */ 66 unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace; 67 #endif /* CONFIG_SMP */ 68 69 /* 70 * Should we panic (and reboot, if panic_timeout= is set) when a 71 * hung task is detected: 72 */ 73 unsigned int __read_mostly sysctl_hung_task_panic = 74 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE; 75 76 static int 77 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr) 78 { 79 did_panic = 1; 80 81 return NOTIFY_DONE; 82 } 83 84 static struct notifier_block panic_block = { 85 .notifier_call = hung_task_panic, 86 }; 87 88 static void check_hung_task(struct task_struct *t, unsigned long timeout) 89 { 90 unsigned long switch_count = t->nvcsw + t->nivcsw; 91 92 /* 93 * Ensure the task is not frozen. 94 * Also, skip vfork and any other user process that freezer should skip. 95 */ 96 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP))) 97 return; 98 99 /* 100 * When a freshly created task is scheduled once, changes its state to 101 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it 102 * musn't be checked. 103 */ 104 if (unlikely(!switch_count)) 105 return; 106 107 if (switch_count != t->last_switch_count) { 108 t->last_switch_count = switch_count; 109 t->last_switch_time = jiffies; 110 return; 111 } 112 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ)) 113 return; 114 115 trace_sched_process_hang(t); 116 117 if (sysctl_hung_task_panic) { 118 console_verbose(); 119 hung_task_show_lock = true; 120 hung_task_call_panic = true; 121 } 122 123 /* 124 * Ok, the task did not get scheduled for more than 2 minutes, 125 * complain: 126 */ 127 if (sysctl_hung_task_warnings) { 128 if (sysctl_hung_task_warnings > 0) 129 sysctl_hung_task_warnings--; 130 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", 131 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ); 132 pr_err(" %s %s %.*s\n", 133 print_tainted(), init_utsname()->release, 134 (int)strcspn(init_utsname()->version, " "), 135 init_utsname()->version); 136 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" 137 " disables this message.\n"); 138 sched_show_task(t); 139 hung_task_show_lock = true; 140 141 if (sysctl_hung_task_all_cpu_backtrace) 142 hung_task_show_all_bt = true; 143 } 144 145 touch_nmi_watchdog(); 146 } 147 148 /* 149 * To avoid extending the RCU grace period for an unbounded amount of time, 150 * periodically exit the critical section and enter a new one. 151 * 152 * For preemptible RCU it is sufficient to call rcu_read_unlock in order 153 * to exit the grace period. For classic RCU, a reschedule is required. 154 */ 155 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t) 156 { 157 bool can_cont; 158 159 get_task_struct(g); 160 get_task_struct(t); 161 rcu_read_unlock(); 162 cond_resched(); 163 rcu_read_lock(); 164 can_cont = pid_alive(g) && pid_alive(t); 165 put_task_struct(t); 166 put_task_struct(g); 167 168 return can_cont; 169 } 170 171 /* 172 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for 173 * a really long time (120 seconds). If that happens, print out 174 * a warning. 175 */ 176 static void check_hung_uninterruptible_tasks(unsigned long timeout) 177 { 178 int max_count = sysctl_hung_task_check_count; 179 unsigned long last_break = jiffies; 180 struct task_struct *g, *t; 181 182 /* 183 * If the system crashed already then all bets are off, 184 * do not report extra hung tasks: 185 */ 186 if (test_taint(TAINT_DIE) || did_panic) 187 return; 188 189 hung_task_show_lock = false; 190 rcu_read_lock(); 191 for_each_process_thread(g, t) { 192 if (!max_count--) 193 goto unlock; 194 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) { 195 if (!rcu_lock_break(g, t)) 196 goto unlock; 197 last_break = jiffies; 198 } 199 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ 200 if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE) 201 check_hung_task(t, timeout); 202 } 203 unlock: 204 rcu_read_unlock(); 205 if (hung_task_show_lock) 206 debug_show_all_locks(); 207 208 if (hung_task_show_all_bt) { 209 hung_task_show_all_bt = false; 210 trigger_all_cpu_backtrace(); 211 } 212 213 if (hung_task_call_panic) 214 panic("hung_task: blocked tasks"); 215 } 216 217 static long hung_timeout_jiffies(unsigned long last_checked, 218 unsigned long timeout) 219 { 220 /* timeout of 0 will disable the watchdog */ 221 return timeout ? last_checked - jiffies + timeout * HZ : 222 MAX_SCHEDULE_TIMEOUT; 223 } 224 225 /* 226 * Process updating of timeout sysctl 227 */ 228 int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, 229 void *buffer, size_t *lenp, loff_t *ppos) 230 { 231 int ret; 232 233 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); 234 235 if (ret || !write) 236 goto out; 237 238 wake_up_process(watchdog_task); 239 240 out: 241 return ret; 242 } 243 244 static atomic_t reset_hung_task = ATOMIC_INIT(0); 245 246 void reset_hung_task_detector(void) 247 { 248 atomic_set(&reset_hung_task, 1); 249 } 250 EXPORT_SYMBOL_GPL(reset_hung_task_detector); 251 252 static bool hung_detector_suspended; 253 254 static int hungtask_pm_notify(struct notifier_block *self, 255 unsigned long action, void *hcpu) 256 { 257 switch (action) { 258 case PM_SUSPEND_PREPARE: 259 case PM_HIBERNATION_PREPARE: 260 case PM_RESTORE_PREPARE: 261 hung_detector_suspended = true; 262 break; 263 case PM_POST_SUSPEND: 264 case PM_POST_HIBERNATION: 265 case PM_POST_RESTORE: 266 hung_detector_suspended = false; 267 break; 268 default: 269 break; 270 } 271 return NOTIFY_OK; 272 } 273 274 /* 275 * kthread which checks for tasks stuck in D state 276 */ 277 static int watchdog(void *dummy) 278 { 279 unsigned long hung_last_checked = jiffies; 280 281 set_user_nice(current, 0); 282 283 for ( ; ; ) { 284 unsigned long timeout = sysctl_hung_task_timeout_secs; 285 unsigned long interval = sysctl_hung_task_check_interval_secs; 286 long t; 287 288 if (interval == 0) 289 interval = timeout; 290 interval = min_t(unsigned long, interval, timeout); 291 t = hung_timeout_jiffies(hung_last_checked, interval); 292 if (t <= 0) { 293 if (!atomic_xchg(&reset_hung_task, 0) && 294 !hung_detector_suspended) 295 check_hung_uninterruptible_tasks(timeout); 296 hung_last_checked = jiffies; 297 continue; 298 } 299 schedule_timeout_interruptible(t); 300 } 301 302 return 0; 303 } 304 305 static int __init hung_task_init(void) 306 { 307 atomic_notifier_chain_register(&panic_notifier_list, &panic_block); 308 309 /* Disable hung task detector on suspend */ 310 pm_notifier(hungtask_pm_notify, 0); 311 312 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd"); 313 314 return 0; 315 } 316 subsys_initcall(hung_task_init); 317